This invention relates to use of signal generators for device security.
Secret keys or other values embedded in devices such as integrated circuits (chips) may be used to authenticate the devices. An example of such an approach uses a secret key embedded in a smart card. This secret key is not intended to be read out, but can be used to decrypt messages sent to the smart card. A service provider who knows the secret key can authenticate the smart card by asking it to decrypt an encrypted message or using other cryptographic protocols that verify that the smart card possesses the key. The secret key needs to remain secret so that an adversary cannot duplicate the key and assume a false identity.
Authentication of integrated circuits has been suggested using device characteristics that vary from device to device based on variation in the fabrication process. Some such approaches, which are based on circuit delay are described in U.S. Application Publication US2003/0204743A1, titled “Authentication of Integrated Circuits,” which is incorporated herein by reference.
One approach to generating a key that is described in US2003/0204743A1 uses a measurement of a frequency of a self-oscillating circuit. Another approach uses a ratio of the measured frequencies of two self-oscillating circuits. Use of a ratio provides some compensation for variations that are due, for example, to environmental conditions of the circuit.